1. Field of the Invention
This invention relates generally to seismic exploration and, more particularly to a system for separating compression waves from shear waves and up-going from down-going waves.
2. Description of the Related Art
A problem encountered in marine seismic surveying, as well as vertical seismic profiling, is that of water column reverberation, or multiple reverberation. Reverberations arise as a result of the inherent reflectivity of boundaries such as the water surface and bottom. A seismic wave generated in, or reflected off of, the earth's strata passes into the water in a generally up-going direction. This reflected wave of interest travels through the water and past the seismic detector or receiver, which records the wave. The wavefield continues upward to the water's surface where it is reflected back in a down-going direction. This reflected, or ghost, wavefield also travels through the water and past the receiver where it is again recorded. This reverberation of the seismic wavefield in the water obscures seismic data, amplifying certain frequencies and attenuating others, thereby making it difficult to analyze the underlying earth formations.
Ruehle, U.S. Pat. No. 4,486,865, incorporated herein by reference, discloses a seismic multiple suppression method employing inverse filters designed from the differing response characteristics of co-located hydrophones and geophones to primary and multiple seismic reflections. Loewenthal et al., U.S. Pat. No. 4,752,916, incorporated herein by reference, proposed the use of co-located hydrophones and geophones to estimate the source wavelet and then to use a deconvolution based on this wavelet to deghost the observed seismic data. Barr, U.S. Pat. No. 4,979,150, incorporated herein by reference, and Barr et al., U.S. Pat. No. 5,163,028, also incorporated herein by reference, disclose methods for reducing multiple reverberations in marine seismic reflection data by calibrating, scaling and summing together co-located hydrophone and geophone seismic data. Dragoset, U.S. Pat. No. 5,365,492, incorporated herein by reference, teaches an improved method of scaling the geophones to the hydrophones based on application of adaptive noise reduction techniques. Moldoveanu, U.S. Pat. No. 5,621,700, incorporated herein by reference, teaches an improved method of attenuation of reverberations by combining reverberation signals having identical amplitudes but opposite polarities wherein the reverberations are cancelled and only primary waves of interest remain.
These methods do not allow for multiple-free, single-component-type (e.g. hydrophone or geophone) data. Thus, there is a need for a process that will allow for a simple production of single-component-type sections.